Coated articles provided for solar control purposes are known in the art. For example, see U.S. Pat. No. 5,344,718, which discloses a layer stack of: glass/Si3N4/NiCr/Ag/NiCr/Si3N4. In coatings such as this, NiCr barrier layers are commonly used to protect the Ag (silver) in low-E type coatings.
Unfortunately, metallic NiCr is characterized by high absorption which reduces transmittance of the final coated article. Due to this high absorption problem, those in the art desiring products with high visible transmission have been forced to use very thin NiCr barrier layers. For example, the NiCr layers in the aforesaid '718 patent are “less than about 7 Å” thick, in order to obtain the desired visible transmission. The thinner such layers are, the less barrier functionality and protection they provide. Consequently, those skilled in the art have been seeking to increase barrier layer transmission by introducing oxygen and/or nitrogen to NiCr barrier layers (e.g., see U.S. Pat. No. 6,014,872 at col. 4, lines 40-50).
Consider a layer stack of glass/Si3N4/NiCrOx/Ag/NiCrOx/Si3N4. While the NiCrOx protective barrier layers are more transparent than NiCr protective barrier layers, they have their problems. For instance, the use of NiCrOx protective barrier layers contacting the Ag layer on respective sides thereof can sometimes lead to problems with respect to durability and/or heat treatability. It is believed that during deposition (e.g., via sputtering) of a coating including NiCrOx protective barrier layers, the Ag layer is exposed to the oxygen plasma (and thus chemically active atomic oxygen in that plasma) used in depositing the NiCrOx; this is especially true with respect to the top surface of the Ag layer when an upper NiCrOx protective barrier is applied directly thereto. The exposure of the Ag to this oxygen inclusive plasma is believed to sometimes lead to Ag adhesion problems.
In view of the above, it will be apparent to those skilled in the art that there exists a need for an improved barrier layer(s) structure for protecting an IR reflecting layer (e.g., Ag).